There is known a technique relating to contactless electric power transmission (no-contact-point electric power transmission) that enables electric power transmission by using electromagnetic induction or the like even when no contact points exist.
For example, Patent Literature 1 relates to a technique that uses electromagnetic induction for charging a portable terminal such as a cellular phone in a contactless manner. Patent Literature 1 describes contactless electric power transmission between a power transmitting device comprising a primary coil and a power receiving device comprising a secondary coil. In the contactless electric power transmission using electromagnetic induction, a transmission distance of electric power is limited to a distance within the range of several millimeters, and position matching between the coils needs to be precisely performed to maintain the transmission efficiency.
Meanwhile, a contactless electric power transmitting method using a magnetic resonance phenomenon (called magnetic resonance method in the following) as described in Patent Literature 2 has been receiving much attention lately. The magnetic resonance method has an advantage in that the power transmission efficiency is not reduced compared with the case of the electromagnetic induction, even when a distance between a primary coil and a secondary coil, and a positional deviation between the coils become large compared with the case of the electromagnetic induction. For this reason, theoretically, one charge stand (power transmitting device) comprising one primary coil can simultaneously transmit electric power to a plurality of portable terminals (power receiving devices) each comprising the secondary coil.